PER2 rs934945: Understanding Your Circadian Rhythm Genetics
The rs934945 variant is a common genetic marker located within the PER2 gene, which plays a central role in regulating the human biological clock. Research indicates that this variant is associated with individual differences in chronotype, influencing whether a person naturally prefers earlier or later sleep timing.
What each genotype means
Typical morning alertness tendency
You carry two copies of the common G allele for the rs934945 variant in the PER2 gene. Small candidate gene studies have observed statistical associations between the G allele and certain morningness subscales, including earlier activity planning and morning alertness. However, overall evidence across diverse populations remains limited and replication in large genome-wide association studies is inconclusive.
Carried by approximately 35% to 45% of individuals globally, being most frequent in populations of African and European ancestry.
Intermediate circadian trait tendency
You carry one copy of the G allele and one copy of the A allele for the rs934945 variant in the PER2 gene. Research investigating this variant suggests heterozygous individuals exhibit intermediate diurnal preferences and circadian phase patterns compared to homozygous genotypes. Findings are derived from small candidate-gene cohorts, so individual effect on daily sleep-wake timing is modest and subject to significant lifestyle influence.
Carried by approximately 45% to 50% of individuals across most world populations.
Slight evening preference tendency
You carry two copies of the minor A allele for the rs934945 variant in the PER2 gene. In candidate gene investigations, the A allele has been linked to lower morning alertness and a slight relative shift toward later diurnal preference. Because current genetic evidence linking this specific locus to chronotype differences is limited and not robustly replicated across large cohorts, lifestyle factors play a much larger role.
Carried by roughly 10% to 15% of individuals globally, with varying prevalence across different ancestral backgrounds.
What is rs934945?
The rs934945 variant is a single nucleotide polymorphism (SNP) situated within the intronic region of the PER2 gene. In genetics, an intronic variant is located in a non-coding section of the gene, meaning it does not directly alter the sequence of the protein produced by the gene. Instead, such variants often influence how a gene is expressed or regulated within the cell. Because rs934945 is a common variant, it is found frequently across diverse human populations. It serves as a genetic marker that researchers use to study the complex architecture of human sleep patterns. By analyzing this specific location in the genome, scientists can better understand the biological underpinnings of why individuals exhibit such wide variation in their daily sleep-wake cycles and overall circadian preferences.
The Role of the PER2 Gene
The PER2 gene, or Period Circadian Regulator 2, is a fundamental component of the molecular clock mechanism that governs circadian rhythms in humans. These rhythms are internal processes that regulate the sleep-wake cycle, hormone release, and body temperature over a roughly 24-hour period. The protein encoded by PER2 acts as a transcriptional repressor, forming part of a feedback loop that keeps the body's internal clock synchronized with the external environment. When the PER2 gene functions optimally, it helps maintain a stable circadian period. Disruptions or variations in this gene can lead to shifts in the timing of this internal clock, which may manifest as differences in chronotype—the natural inclination to be a 'morning person' or an 'evening person.' Because of its central role, PER2 is a primary focus for researchers studying sleep-wake phase disorders and the genetic basis of human behavior.
Research and Evidence
Scientific research has established a link between variations in the PER2 gene and human circadian traits. Large-scale genome-wide association studies (GWAS) have identified signals near the PER2 gene that correlate with chronotype and sleep timing. While the evidence for these associations is considered moderate, it highlights the polygenic nature of sleep, meaning that many different genetic variants contribute to an individual's sleep habits. It is important to note that while rs934945 is associated with these traits, it is not a diagnostic tool. Sleep patterns are influenced by a complex interplay of genetics, environmental factors, and lifestyle choices. Current research continues to explore how these specific genetic markers interact with light exposure and social schedules to shape our daily rhythms. As with all genetic associations, these findings represent statistical trends across large populations rather than deterministic outcomes for any single individual.
Interpreting Your Information
Understanding your genetic predisposition regarding sleep can be an interesting way to learn about your biological tendencies, but it is not a substitute for medical advice. If you are experiencing significant sleep disturbances, such as chronic insomnia or extreme difficulty waking up, you should consult a healthcare professional or a sleep specialist. Genetic information cannot diagnose a sleep disorder or predict your exact sleep schedule. Instead, it provides a glimpse into the biological factors that might influence your natural preferences. You cannot change your genetic code, but knowing your chronotype can help you make informed lifestyle choices, such as adjusting your work schedule or light exposure to better align with your internal clock. Always prioritize clinical guidance over genetic reports when addressing health concerns, and never use this information to make decisions about medication or treatment without speaking to your doctor.
How common is this variant?
The rs934945 variant is a common polymorphism, with its specific genotypes appearing at varying frequencies across different global ancestral populations.
Frequently asked questions
Can this variant tell me if I have a sleep disorder?
No, this variant cannot diagnose a sleep disorder. It is only associated with natural variations in chronotype and sleep timing, not with clinical pathology.
Does having a specific genotype mean I will be a night owl?
Genetics is only one factor in determining your sleep habits. While certain variants are associated with later sleep timing, your environment and lifestyle also play significant roles.
Should I change my sleep schedule based on my genotype?
You should prioritize your health and well-being over genetic data. If you are concerned about your sleep quality, consult a doctor rather than making changes based on a genetic report.
Is PER2 the only gene that affects sleep?
No, sleep is a complex trait influenced by many genes, including other clock genes like PER3, CRY1, and ARNTL. No single gene determines your entire sleep profile.
Sources & further reading
Educational information only, last refreshed 10/9/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Pathogenic missense variant (Ser662Gly) in PER2 that impairs casein kinase phosphorylation, causing familial advanced sleep phase syndrome (FASPS-1).
Common missense/synonymous tagging variant in core clock gene PER2 modulating eveningness preference and diurnal phase delay.
Variant in the circadian regulator PER2 associated with circadian rhythm phase, chronotype, and timing of habitual sleep.
This variant is associated with familial advanced sleep phase syndrome, affecting the timing of the sleep-wake cycle.
A mutation in the PER2 gene associated with familial advanced sleep phase syndrome, leading to an earlier sleep-wake cycle.
An intronic single-nucleotide variant in the core clock gene PER2 recently identified in familial delayed sleep phase syndrome and evening chronotypes.